The present invention pertains to communications and networking. More particularly, the invention relates to the usage of resources in networking devices.
FIG. 1A shows an example of a prior art wide-area networking system serviced by ATM (Asynchronous Transfer Mode). A wide-area network (WAN) link 120 interconnects a first network 100 with a second network 110. Each network has a plurality of nodes which may each contain switching devices that regulate data traffic to one or more user terminals. Network 100 is shown having nodes 102, 103, 104, 106, and 108, while network 110 is shown having nodes 112, 114, 116, and 118. A first user terminal 105 is connected to node 102 of network 100 and a second user terminal 115 is connected to node 118 of network 110. In order for user terminal 105 and user terminal 115 to communicate with each other, a call must first be established between them. This call may be switched through a plurality of nodes. One possible route for sending data from user terminal 105 to user terminal 115 is for data to go from node 102 to 106 to 108 and then across the WAN link to node 112 and node 118, finally reaching user terminal 115.
Each node has a controller device and switch which facilitate the calls through the node. The controller has processing, memory, and other resources to interpret, forward, and process messages and initiate other messages as appropriate, while the switch ordinarily handles the physical routing of messages among nodes and user terminals.
In a redundant high-availability private network-to-network interface (xe2x80x9cPNNIxe2x80x9d) routing protocol implementation, a redundant pair of controllers is used in the case of controller failure. Thus, each node has two controllers, one primary and one secondary. In order to ensure the proper functioning of the secondary controller in case the primary controller fails, it is desirable to test the secondary controller by switching the primary controller to a standby state and the secondary controller to an active state. The switching of controllers is also desirable for performing maintenance on the primary controller.
A secondary controller follows the state of the primary controller with a slight delayxe2x80x94for example, a delay of one second. During a switchover, all activity must be transferred from the primary controller to the secondary controller. However, because of the delay between the controllers, synchronization of the controllers can not be guaranteed. A small delay such as this could cause destabilization of the network.
FIG. 1B shows an example of a prior art node configuration. When messages of any type are received at the node at a particular interface, they first pass through switch 150 and then are forwarded to the layer 2 function of secondary controller 160 or of primary controller 165 depending on which controller is active. The layer 2 function of controllers 160 and 165 is also referred to as SSCOP (Service-Specific Connection-Oriented Protocol, set forth in the ITU (International Telecommunication Union) specifications Q.2110 (B-ISDN ATM adaptation layer-service Specific Connection Oriented Protocol (SSCOP) 07/94) and Q.2130 (B-ISDN signaling ATM adaptation layer-Service Specific coordination function for support of signaling at the user network interface (SSFC At UNI) 07/94), which provides a reliable data link transport function to layer 3. The layer 3 function performs both signaling and call processing. Not shown is an intermediary buffer between layer 2 and layer 3 which is incorporated for sequencing and timing in some systems.
Because of the synchronization delay described above, SSCOP sessions may go down and communication with other nodes may be broken. When an SSCOP session goes down, ATM protocols require a status enquiry to be performed. The status enquiry resynchronizes all connections to the downed node with all its neighboring nodes. A node often has between 500,000 and 1,000,000 connections to resynchronize. If the synchronization does not occur quickly, all calls going to the downed node may be lost. It is desirable to avoid the status enquiry procedure because the procedure generates a flurry of status messages in the networkxe2x80x94for example, if eight messages per connection are sent and the node maintains 100,000 connections, then 800,000 messages would be sent, which can cause a destabilization of the node.
For these reasons, switches have been typically operated on the same active primary card for extended periods of time. When the switchover is forced to occur, if a secondary controller is not operational, the primary controller has to be reset and the databases of the primary controller have to be rebuilt, causing hours of network outages.
What is disclosed is a method for switching from a primary network controller to a secondary network controller. A switchover request is received. Messages accepted by the node from the peer nodes are limited. An active link is maintained between the node and peer nodes. Finally, control is transferred from the primary controller to the secondary controller.
Other features and advantages of the present invention will be apparent from the accompanying drawings and from the detailed description that follows below.